1. Field of the Invention
The present invention relates to a triphenylene based aromatic compound, and in particular relates to an organic light emitting diode utilizing the same.
2. Description of the Related Art
The earliest report of organic electroluminescence was made by Pope et al in 1963, who observed a blue fluorescence from 10-20 μm of crystalline anthracene by applying voltage across opposite sides of the crystal. Thus, starting a wave of first improvements in organic electroluminescence research. However, difficulties of growing large areas of crystals were a challenge. The driving voltage of the device was too high and the efficiency of organic materials was lower than inorganic material. Because of the disadvantages of the devices, the devices were not widely applied due to practical purposes.
However, a major development in organic electroluminescence technology was reported in 1987. Tang and VanSlyke of Eastman Kodak Company used vacuum vapor deposition and novel hetero junction techniques to prepare a multilayered device with hole/electron transporting layers. 4,4-(cyclohexane-1,1-diyl)bis(N,N-dip-tolylbenzenamine) (TPAC) was used as a hole transporting layer, and Alq3 (tris(8-hydroxyquinolinato) aluminum(III)) film with good film-forming properties was used as an electron transporting and emitting layer. A 60-70 nm-thick film was deposited by vacuum vapor deposition with a low-work function Mg:Ag alloy as a cathode for efficient electron and hole injections. The bi-organic-layer structure allowed the holes and electrons to recombine at the p-n interface and then emit light. The device emitted green light of 520 nm, and was characterized by low driving voltage (<10 V), high quantum efficiency (>1%) and good stability. The improvements, once again, arouse interest in organic electroluminescence research.
Meanwhile, Calvendisg and Burroughes et al. at Cambridge University in 1990 was the first to report using conjugated polymer PPV (poly(phenylene vinylene)) as an emitting layer in a single-layered device structure by solution spin coating. The development of an emitting layer with conjugated polymer drew great interest and quickly sparked research due to the simplicity of fabrication, good mechanical properties of polymer, and semiconductor-like properties. In addition, a large number of organic polymers are known to have high fluorescence efficiencies.
In U.S. patent application Ser. No. 11/968,353, the inventor of the invention had disclosed the triphenylene derivatives application in blue light emitting device. In previously application, the aromatic center had two substituents such as triphenylenyl group, pyrenyl group, or combinations thereof. When the aromatic center was benzene, the two substituents were para-substituted on the benzene. This application only focused on tuning the center aromatic types, however, it did not disclose the different substituted positions of the substituents and the influences thereof.
Accordingly, methods and corresponding formulae are called for to reduce the symmetry of the triphenylene based aromatic compound. In addition, the methods without largely changing the synthetic steps and the corresponding formulae may enhance the thermal stability (such as Tg) and luminescence property (such as external quantum efficiency) of the device utilizing the triphenylene based aromatic compound.